The main problem is that over time you become more and more sensitive to it. So even if initially you have no response don't be surprised if after some time of using it regularly you have really bad allergic reactions to even mild exposure.
(For boatbuilding, the usual choice is polyester resin rather than epoxy, which is nasty in other ways. You don't wanna be inhaling those styrene vapors all day long.)
I got a kit with some fiberglass to fix a cracked bumper on a car. Don't want to do that ever again.
Epoxy is highly allergenic (or whatever the word is), so you should be pretty careful about using nitrile gloves or similar when working with it. Personally I don't find the smell particularly bad, and it's not very strong, at least compared to polyester resin.
Polyester, yes it smells bad, and as I mentioned in my parent comment that's styrene vapors you're inhaling, which is a known carcinogen. If I were to do some bigger job with polyester, I'd definitely want some pretty hefty breathing filter. But for the occasional one-off thing, particularly if you can do it outdoors, meh..
AFAIK most allergies/hypersensitives are for harmless things; animals, pollen, and different types of food. So basing what we grow sensitive to might not be the best test to see if a product can cause harm